Staphylococcus aureus is one of the major bacterial pathogens in both community and clinical settings causing disease in human with substantial morbidity and mortality. The recent emergence of vancomycin and community-associated methicillin resistance S. aureus strains has further highlighted the importance of new targets identification for the development of novel therapeutic agents. The pathogenesis of Staphylococcus is a complex process that involves multiple virulence factors;therefore, it is not surprising that an effective therapeutic strategy directed against a single factor has not been highly successful against this organism. To deal with the emergence of antibiotic resistant strains and to target this organism in general, a useful tactic may be to disrupt the global regulatory pathways, singly or in combination, to minimize the expression of extracellular and cell surface associated factors in vivo. To understand control of staphylococcal gene expression in relation to virulence, we will continue to focus on the SarA family transcriptional regulators because of its central role in staphylococcal genetic and pathogenesis and in control of the regulatory networks in Staphylococcus. The precise mechanism by which this family of genes is regulated and regulates their target genes is largely unknown. Our long-term research goal is to understand the regulation of sarA-family genes and virulence factors regulated by the SarA family proteins in Staphylococcus. This regulation can be accomplished by site-specific binding of SarA proteins or by the environmental factors. One key impediment to interpreting the sar-family related data is that a majority of results are derived from in vitro studies. It has been reported that in vitro vs. in vivo disparities exist in gene expression profiles and organ-specific gene expression regulatory paradigms for a given gene. We believe some of the sarA paralogs may have differential expression pattern in vivo as compared to that of in vitro and may have important consequences for virulence or infection processes. Therefore, we propose to determine the involvement and significance of sarA-family genes in mouse infection model and compare in vivo and in vitro expression profiles of sarA-family genes in one important clinical strain the hospital- associated MRSA COL. The experimental findings of this proposal will be very useful to understand and develop SarA paralogs targeted therapeutic agents to prevent or cure Staphylococcus infections. PUBLIC HEALTH RELEVANCE: To understand control of staphylococcal gene expression in relation to virulence, we will continue to focus on the SarA family transcriptional regulators because of its central role in staphylococcal genetic and pathogenesis and in control of the regulatory networks in Staphylococcus. Staphylococcal specific sarA family genes are emerging as potential targets for therapeutic intervention, but their mode of regulation and involvement in virulence process are largely unknown. Therefore, our major aims of this proposal will be to determine in vivo significance and the expression of sarA-family genes during infection process.